Engineering Papers⌕ Search

Engineering topics

Tokunaga, A. T.

Publications and source records attributed to Tokunaga, A. T..

99 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

The 20-micron brightness temperature of the unilluminated side of Saturn's rings

Observations of the 20-micron brightness temperature of the unilluminated (north) side of Saturn's rings are presented and discussed in terms of models of B ring heating. Observations centered on the B ring ansae were made at 19.8 microns by the 3-m IR telescope facility on Mauna Kea during a period when the unilluminated side of the rings could be observed from earth. Flux measurements indicate a 20-micron brightness temperature of 56 + or - 1 K, in agreement with that measured at 45 microns by Pioneer 11. Under the assumptions that the emission of the Cassini division is negligible and that the ring brightness temperature is close to the actual temperature, it is shown that the brightness temperature can be accounted for by heating by the disk of Saturn, and is proportional to the sine of the Saturnicentric declination of the sun.

Tokunaga, A. T.↗
NASA NTRS1980

Far-infrared spectra of W51-IRS 2 and W49 NW

Measurements of the far-infrared spectra of the powerful H II regions W51-IRS 2 and W49 NW from 65 to 345 per cm with about 9 per cm resolution were obtained by using an airborne Michelson interferometer. The most remarkable feature of the far-infrared spectra of the two regions is the smoothness of the continuum; no evidence is found in the spectra for features of H2O ice at 45 and 62 microns. The spectrum of W51 is well fitted by a 70 K blackbody with a diameter of 14 arc sec, but the spectrum of W49 NW is narrower than a blackbody. The implications of the apparently high peak optical depths of these sources are discussed.

Erickson, E. F.↗
NASA NTRS1980

IR brightness and eclipse cooling of Saturn's rings

Equatorial scans of Saturn at 20 microns wavelength, obtained with the Mayall 4-m telescope in 1978-79, show a continuing decrease in the specific brightness of the A and B rings as the ring plane projection approaches and edge-on apparition. The decreased brightness of the previously dominant B ring reveals more clearly a large difference in brightness between the east and west ansae portions of the C ring, in contrast to a barely discernible difference for the other ring ansae. The amount of eclipse cooling is compatible with a C ring particle size of about 1 cm. It is proposed here that the B ring brightness variation could partially result from a decrease of absorbed insolation by a modest amount of visible scattering.

Nolt, I. G.↗
NASA NTRS1979

Temporal characteristics of the Jovian atmosphere

Drift scans along the central meridian of Jupiter have been obtained at wavelengths of 7.9, 17.8, and 19.7 microns. These observations indicate a significant north-south temperature asymmetry within the Jovian stratosphere but not within its troposphere, results which agree with the recent Voyager 1 observations. Employing a time-dependent stratospheric model, it is found that the observed north-south asymmetry is consistent with seasonal stratospheric variability. In the model, the primary cause for this variability is the time-dependent absorption of sunlight by aerosols.

Caldwell, J.↗
NASA NTRS1979

The mean Jovian temperature structure derived from spectral observations from 105 to 630 cm kaysers

Far infrared observations of the thermal emission of Jupiter are used to determine the temperature at 1 bar. High-altitude observations of the whole-disk brightness temperature of Jupiter in the range of 100 to 347 kaysers were inverted to obtain a P-T profile between 1.5 and 0.06 atm, assuming as opacity sources the H2 collisionally induced continuum and the rotation inversion bands of ammonia. The P-T profile derived from the spectrum reproduces the main features of the observed spectrum, with a slightly improved fit if the effects of ammonia haze opacity or NH3 supersaturation in the saturated region are taken into account. The Jovian temperature is found to be 160 + or - 7 K at 1 bar, and 105 + or - 3 K at the inversion level at 0.15 bar. The 1-bar temperature is shown to be consistent with Jovian interior models which match the observed gravitational moment.

Goorvitch, D.↗
NASA NTRS1979

High-resolution spectra of Jupiter in the 744-980 inverse centimeter spectral range

Spectra of the central 5 in region of Jupiter in the 744 to 980 kayser spectral range are presented at 0.05 and 0.28 kayser resolution. The gases (N-14)H3, (N-15)H3, and PH3 are observed in absorption, and C2H2 and C2H6 observed in emission. A synthetic spectrum which included the opacity from the H2, (N-14)H3, (N-15)H3, and PH3 is compared with observations. It is concluded that: (1) the (N-14)H3 line profiles are best fitted with a NH3 density in the troposphere which is 0.5 times the saturated vapor pressure density and an opaque cloud at the 0.56 bar pressure level, (2) the best fit (N-15)H3/(N-14)H3 ratio is 0.006, (3) the PH3/H2 abundance ratios of NH3 and PH3 must be highly subsaturated above the tropopause or the temperature inversion is cooler than model predictions.

Tokunaga, A. T.↗
NASA NTRS1979

Spatially resolved infrared observations of Saturn. III - 10- and 20-micron disk scans at B prime = -11.8 deg

Disk scans of Saturn at 10 and 20 microns were obtained when the Saturnicentric solar declination B prime was -11.8 deg. The scans show little change from scans obtained when B prime was -16.3 deg. This could result from the long radiative time constant of the Saturnian atmosphere. The observations at 20 microns, in the H2 continuum, show positively that the temperature inversion at the south pole has a higher temperature than at any other point on the disk. In addition, the 12.1- and 20-micron scans indicate that the temperature of the inversion region is higher at the equator compared to the temperate zone. The data also suggest that enhanced 20-micron emission is correlated with the strength of the ultraviolet absorption.

Tokunaga, A. T.↗
NASA NTRS1978

The far-infrared spectrum of S140 IR

The spectrum of S140 IR from 65 to 345 kaysers (155-29 microns) has been measured with 9.4-kayser resolution. The emission in this spectral range is consistent with a 9-arcsec-diameter blackbody radiating at a temperature of 70 K. Attempts at finding a self-consistent radiative-transfer model of the source suggest that the near- and far-infrared observations cannot result from a spherically symmetric nebula with a continuous density distribution and a central exciting source. A number of compact near-infrared sources may be embedded in the cloud.

Tokunaga, A. T.↗